A ball fracturing sliding sleeve capable of being fished in multiple stages in series and capable of being repeatedly opened and closed

Abstract

This utility model relates to the field of downhole oilfield completion tools, specifically to a ball-drop fracturing sliding sleeve capable of multi-stage tandem retrieval and repeated opening and closing. It includes: an upper connector and a lower connector fixedly connected to each other and forming an outer shell, with cavities formed inside the upper and lower connectors; and a sliding sleeve slidably disposed within the cavities. The upper connector has fracturing through holes on its sidewall. Through the left-hand serrated thread engagement between the ratchet connector and the sealing retrieval head, while retrieving the current stage's inner ball seat unit, the next stage's inner ball seat unit can be retrieved downwards. All multi-stage ball seat assemblies can be retrieved in a single trip, achieving multi-stage tandem retrieval. Furthermore, the ratchet connector thread uses a special angled left-hand serrated tooth profile, and the bearing tooth side angle ensures axial tensile strength. If obstruction occurs during retrieval and the tubing is pulled too far to the string limit, the tool can be released from the obstruction point by right-handing the tubing string, allowing the tool above the obstruction point to be retrieved from the well.

Description

Technical Field

[0001] This utility model relates to the field of downhole oilfield completion tools, and in particular to a ball-dropping fracturing sliding sleeve that can be retrieved in multiple stages and can be repeatedly switched on and off. Background Technology

[0002] In the field of downhole oilfield completion, ball-drop fracturing sleeve is one of the core tools for implementing segmented fracturing. During construction, balls of different sizes are dropped in stages to open the fracturing channels of each segment of the sleeve in sequence, and fracturing fluid is injected into the target formation to achieve the transformation of multiple segments one by one. After fracturing is completed, the ball seat inside the sleeve needs to be removed to restore the full-bore production channel.

[0003] To overcome the problems of long operation cycles and high risk of stuck drill bits caused by drilling and grinding to remove ball seats, existing technologies have developed ball-drop fracturing sleeves capable of retrieving ball seats. Some of these solutions further achieve multi-stage tandem retrieval, meaning that each stage of ball seat can be retrieved in a single trip, reducing the number of trips. However, these tandem retrieval solutions all use a spring-claw locking mechanism to connect the upper and lower stages. While this can complete tandem retrieval under normal operating conditions, if obstruction is encountered during retrieval, the spring-claw locking structure cannot actively disengage, causing the entire tandem series to become stuck. This can only be resolved by force lifting or reverse clamping, resulting in high operational risks and potentially causing downhole accidents in severe cases. Utility Model Content

[0004] In view of this, the purpose of this utility model is to propose a ball-throwing fracturing sleeve that can be used for multi-stage series retrieval and can be repeatedly switched on and off, so as to realize multi-stage series retrieval to improve the operation efficiency, while ensuring that each stage can actively release itself when encountering obstruction to avoid the drill getting stuck.

[0005] To achieve the above objectives, this utility model provides a ball-dropping fracturing sleeve capable of multi-stage series salvage and repeated opening and closing, comprising:

[0006] An upper connector and a lower connector are fixedly connected to each other and form an outer shell, and cavities are formed inside the upper connector and the lower connector.

[0007] A sliding sleeve is slidably disposed in the cavity, and a fracturing through hole is provided on the side wall of the upper connector. The sliding sleeve blocks the fracturing through hole in the initial position.

[0008] The inner ball seat unit, which is detachably disposed inside the sliding sleeve, includes a sealing head, a bridge body, an elastic sleeve, a connecting body, a ball seat, and a pawl joint connected in series. The upper inner wall of the sealing head is provided with a first left-hand sawtooth thread for docking with the anchor. The outer circle of the pawl joint is provided with a second left-hand sawtooth thread that matches the first left-hand sawtooth thread on the inner wall of the next-level sliding sleeve sealing head, so as to realize the series retrieval of multiple inner ball seat units, and can be unscrewed and released by right-handed tubing when encountering obstruction.

[0009] As a preferred embodiment of this utility model, the inner ball seat unit is detachably suspended inside the sliding sleeve via an elastic sleeve; elastic claws are distributed circumferentially at the upper end of the elastic sleeve, and each elastic claw has an outwardly protruding boss at its upper end. In the initial state, the boss is engaged in the damping elastic claw groove provided on the inner wall of the sliding sleeve; the lower outer circle of the sealing head expands the elastic claws in the initial state, so that the boss is kept engaged with the damping elastic claw groove.

[0010] As a preferred technical solution of this utility model, the bridge body and the elastic sleeve are fixedly connected by a second shear screw; when the lifting and retrieval is performed, the second shear screw is cut off, the sealing retrieval head moves upward relative to the elastic sleeve, the supporting effect of the lower outer circle of the sealing retrieval head on the elastic claw is released, the elastic claw retracts inward, the boss disengages from the damping claw groove, and the inner ball seat unit disengages from the sliding sleeve.

[0011] As a preferred technical solution of this utility model, the second left-hand sawtooth thread of the ratchet joint has a sharp bevel angle and a small root angle, which is used to guide the ratchet joint to smoothly enter the internal thread of the next sealing head during normal lowering, and to ensure axial load stability after engagement.

[0012] As a preferred technical solution of this utility model, the pawl joint has an axially extending long groove on its circumference, dividing the front end of the pawl joint into multiple circumferentially evenly distributed pawl pieces, and each pawl piece has a groove to improve its radial elastic deformation capability.

[0013] As a preferred technical solution of this utility model, the lower end of the sliding sleeve is cut with a long groove to form circumferentially distributed damping claws; when the sliding sleeve moves down to the open position after being pressed by the ball, the damping claws are engaged in the damping claw groove provided on the inner wall of the lower connector, which is used to prevent the sliding sleeve from axially displacing when retrieving the inner ball seat unit.

[0014] As a preferred embodiment of this utility model, the sliding sleeve is fixed inside the upper connector by a first shearing screw; when the ball is thrown and sits on the ball seat, the first shearing screw is sheared by pressing the column to a predetermined pressure, and the sliding sleeve slides downward to expose the fracturing through hole.

[0015] As a preferred technical solution of this utility model, the inner wall of the sliding sleeve is also provided with a switch tool slot, which is used to engage with the locking block of a special sliding sleeve opening or closing tool after the inner ball seat unit is retrieved from the well. By lifting or lowering the tubing string, the sliding sleeve is pulled to move axially, so as to realize the reopening or closing of the fracturing through hole.

[0016] The beneficial effects of this utility model are as follows: Through the left-hand sawtooth thread engagement between the pawl connector and the sealing retrieval head, while retrieving the current level of inner ball seat unit, it is possible to continue to retrieve the next level of inner ball seat unit downwards. All multi-level ball seat assemblies can be retrieved in one trip, realizing multi-level tandem retrieval. Moreover, the pawl connector thread adopts a left-hand sawtooth tooth profile with a special angle, and the bearing tooth side angle ensures axial tensile strength. If the retrieval process encounters obstruction and the tubing is pulled too far to the limit, it can be released from the obstruction point by using a right-handed tubing string, and the tool above the obstruction point can be retrieved from the well. Then, a tool with a higher load capacity can be lowered to continue retrieving the remaining inner ball seat units, avoiding the risk of the tool getting stuck downhole. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the overall half-section structure of this utility model;

[0019] Figure 2 This is a partial cross-sectional view of the inner ball seat unit of this utility model.

[0020] Figure 3 This is a half-sectional structural diagram of the sliding sleeve of this utility model;

[0021] Figure 4 This is a half-sectional structural diagram of the elastic sleeve of this utility model;

[0022] Figure 5 This is a schematic diagram of the half-section structure of the anchor-retrieval device of this utility model;

[0023] Figure 6 This is a half-sectional structural diagram of the opening tool of this utility model;

[0024] Figure 7 This is a half-sectional view of the closing tool of this utility model;

[0025] Figure 8 For the present utility model Figure 1 A magnified view of the partial result at point A in the middle;

[0026] Figure 9 For the present utility model Figure 1 A magnified view of the partial result at point B in the middle;

[0027] Figure 10 For the present utility model Figure 1 A magnified view of the partial result at point C.

[0028] The markings in the diagram are as follows: 1. Upper connector; 101. Fracturing through hole; 102. First shear screw hole; 103. Third damping spring claw groove; 2. O-ring 2; 3. Sliding sleeve; 301. Switch tool slot; 302. First damping spring claw groove; 303. Annular shear groove; 304. Damping spring claw; 4. Sealing head; 5. Seventh O-ring; 6. Eighth O-ring; 7. First shear screw; 8. Second O-ring; 9. Bridge body; 10. Second shear screw; 11. Third O-ring 12. Fourth O-ring seal; 13. Fifth O-ring seal; 14. First O-ring seal; 15. Elastic sleeve; 1501. Elastic claw plate; 1502. Second shear pin hole; 1503. Set screw hole; 16. Socket head cap set screw; 17. Connector; 18. Lower connector; 1801. Second damping elastic claw groove; 19. Sixth O-ring seal; 20. Pawl connector; 21. Ball seat; 22. Ball thrower; 23. Anchor retrieval upper connector; 24. Anchor retrieval connector; 25. Stop pin. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to specific embodiments.

[0030] It should be noted that, unless otherwise defined, the technical or scientific terms used in this utility model should have the ordinary meaning understood by one of ordinary skill in the art to which this utility model pertains. The terms "first," "second," and similar terms used in this utility model do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0031] like Figures 1 to 10As shown, this utility model discloses a ball-drop fracturing sliding sleeve capable of multi-stage series retrieval and repeated opening and closing. The sleeve mainly consists of four parts: an upper connector 1, a lower connector 18, a sliding sleeve 3, and an inner ball seat unit. The upper connector 1 and lower connector 18 are fixed together by threads to form an outer shell. The sliding sleeve 3 is installed in the cavity formed by the upper connector 1 and lower connector 18 and can slide axially. The inner ball seat unit is installed inside the sliding sleeve 3 and is detachably suspended and fixed to the sliding sleeve 3 by elastic claws. In addition, this utility model also includes three specialized operating tools: a retrieval anchor, an opening tool, and a closing tool.

[0032] The upper connector 1 is a cylindrical structure with a through-hole running vertically through it. The upper circumference of the upper connector 1 has evenly distributed fracturing through holes 101, and the wall of the upper connector 1 has evenly distributed first shear screw holes 102. The lower end of the upper connector 1 has a third damping spring claw groove 103 corresponding to the closed state of the sliding sleeve. The lower end of the upper connector 1 has an external thread, and the root of the thread has a sealing O-ring groove for installing a first O-ring seal 14 to isolate the inner cavity. The lower connector 18 is fixedly connected to the lower end of the upper connector 1 by threads, and the inner wall of the lower connector 18 has a second damping spring claw groove 1801.

[0033] The sliding sleeve 3 is a cylindrical structure installed inside the upper connector 1. Its outer wall is provided with an annular shearing groove 303, and it is fixed to the upper connector 1 by the first shearing screw 7. The upper outer wall of the sliding sleeve 3 is provided with sealing O-ring grooves on the upper and lower sides corresponding to the fracturing through hole 101 of the upper connector 1 for installing O-ring seals 2. This is used to isolate the inner cavity of the oil pipe from the annulus when the tool is closed, and at the same time seal and isolate the shearing hole.

[0034] The inner wall of the sliding sleeve 3 has an annular first damping claw groove 302 in the middle, and the lower part is formed by cutting a long groove to form circumferentially distributed damping claws 304. When the ball 22 presses down and shears the first shearing screw 7, the sliding sleeve 3 moves downward to the lower connector 18, and the damping claws 304 at its lower end are engaged in the second damping claw groove 1801 provided in the inner wall of the lower connector 18, ensuring that the sliding sleeve 3 will not be displaced when the inner ball seat unit is subsequently retrieved.

[0035] The inner hole of the sliding sleeve 3 is also provided with a switching tool slot 301. After the inner ball seat unit is retrieved from the well, the slot can be used with a special sliding sleeve opening or closing tool. By engaging the locking block of the tool with the switching tool slot 301, the sliding sleeve 3 can be moved by lifting or lowering the tubing string, thereby realizing the re-closing or opening of the fracturing through hole 101.

[0036] The inner ball seat unit is installed inside the sliding sleeve 3 and consists of six parts connected in series: the sealing head 4, the bridge body 9, the elastic sleeve 15, the connector 17, the ball seat 21, and the pawl joint 20. Each part will be described in detail below.

[0037] The sealing head 4 has a cylindrical structure. Its upper inner wall is provided with left-handed sawtooth threads evenly spaced by at least one semicircular groove, serving as the retrieval interface for docking with the retrieval anchor. The outer circumference of the sealing head 4 has a sealing O-ring groove for installing a second O-ring 8, used to achieve a seal between the sliding sleeve 3 and the inner ball seat unit. The lower end face of the sealing head 4 is machined with a chamfered structure to limit the retracted elastic claw 1501 during tool insertion, preventing accidental radial opening of the claw.

[0038] The bridge body 9 is a cylindrical structure. Its upper end is fixedly connected to the lower end of the sealing head 4 via threads, and a sealing O-ring groove is provided at the contact point for installing the third O-ring 11. An annular space is formed between the outer wall of the bridge body 9 and the inner wall of the sliding sleeve 3 to accommodate the elastic sleeve 15. A sealing O-ring groove is provided on the lower inner wall of the bridge body 9 for installing the fourth O-ring 12, which is tightly engaged with the upper outer circle of the ball seat 21. A second shear screw groove is provided in the middle of the lower end of the bridge body 9, and the bridge body 9 is fixed to the elastic sleeve 15 by the second shear screw 10. A sealing O-ring dovetail groove is also provided at the lower end of the bridge body 9 for installing the fifth O-ring 13.

[0039] The elastic sleeve 15 is installed in the annular space between the outer wall of the bridge body 9 and the inner wall of the sliding sleeve 3. Elastic claw plates 1501 are circumferentially distributed on the upper end of the elastic sleeve 15, and each elastic claw plate 1501 has an outwardly protruding boss at its upper end. In the initial assembly state, the lower outer circle of the sealing head 4 expands the elastic claw plate 1501, causing the boss to engage with the first damping claw groove 302 in the middle of the inner wall of the sliding sleeve 3, thereby fixing the entire inner ball seat unit inside the sliding sleeve 3. Second shear pin holes 1502 are evenly distributed around the middle circumference of the elastic sleeve 15 for installing second shear screws 10. The lower inner wall of the elastic sleeve 15 is threaded for connecting the connecting body 17. The bottom end of the elastic sleeve 15 has a set screw hole 1503, which is further fixed to the connecting body 17 by a hexagonal socket set screw 16 to prevent loosening.

[0040] The connector 17 is a cylindrical structure, with threads on its upper outer wall to connect to the lower inner wall of the elastic sleeve 15. The upper inner wall of the connector 17 is threaded for connecting to the ball seat 21, and the lower inner wall is threaded for connecting to the ratchet connector 20. The lower outer circumference of the connector 17 has a dovetail-shaped O-ring groove for installing the sixth O-ring seal 19.

[0041] The ball seat 21 has a cylindrical structure with a large inlet angle at the upper inner side to facilitate the smooth entry of the ball 22. The lower end is equipped with a metal sealing surface of various sizes that can be selected as needed to receive the ball 22 to establish a seal and apply pressure.

[0042] The outer circumference of the ratchet connector 20 features a left-hand sawtooth thread with a sharp bevel angle and a small thread root angle. This design allows the ratchet connector 20 to be better inserted into the sealing retrieval head 4 while also ensuring a more stable retrieval support structure. Circumferentially distributed long grooves divide the front end of the ratchet connector 20 into uniformly sized ratchet claws. Each claw has equally sized grooves to enhance its elastic deformation capability.

[0043] This utility model is equipped with three special working tools, which are used for retrieving the inner ball seat unit, closing the sliding sleeve later, and opening the sliding sleeve later.

[0044] The retrieval anchor is used to retrieve the inner ball seat unit after fracturing operations. The retrieval anchor consists of an upper retrieval anchor connector 23, a retrieval anchor connecting body 24, a stop pin 25, and a ratchet connector 20. The upper retrieval anchor connector 23 is cylindrical, with a tool thread at the upper inner hole for connection to the retrieval tubing, and a thread at the lower inner hole for fixed connection to the retrieval anchor connecting body 24. A wedge angle is provided on the lower end face. The retrieval anchor connecting body 24 is cylindrical, with a thread at the upper outer circumference for fixed connection to the upper retrieval anchor connector 23. A wedge angle is provided at the bottom of the thread to mate with the upper retrieval anchor connector 23. A groove for the stop pin 25 is provided at the upper end, and a thread on the lower inner wall for connection to the ratchet connector 20 is provided. A dovetail-shaped O-ring groove is provided on the lower outer circumference for installing the sixth O-ring seal 19. The stop pin 25 is cylindrical, with cylindrical heads at both ends matching the groove. Its function is to prevent the ball 22 inside the ball seat 21 from popping out when the inner ball seat unit is lifted for retrieval, thus avoiding inconvenience during operations.

[0045] The opening tool is used to reopen the closed sliding sleeve after the inner ball seat unit has been retrieved. The closing tool is used to close the opened sliding sleeve again after the inner ball seat unit has been retrieved. Both the opening and closing tools are run into the well via coiled tubing. After positioning, their locking blocks open and engage with the switching tool slot 301 of the sliding sleeve 3. By lifting or lowering the tubing string, the sliding sleeve 3 is moved, thereby exposing or concealing the fracturing through-hole 101.

[0046] The working principle of this utility model is explained in three parts: the fracturing construction stage, the ball seat retrieval stage, and the post-control stage.

[0047] During the fracturing operation, the sliding sleeve is first lowered into the designed formation along with the completion string. During operation, a ball 22 matching the size of the ball seat 21 is dropped from the wellhead and pumped to sit on the sealing surface of the ball seat 21. Then, pressure is applied from the surface through the tubing. When the pressure reaches the designed value, the first shear screw 7 is sheared, and the sliding sleeve 3 moves downwards under hydraulic pressure, exposing the fracturing through-hole 101 on the upper connector 1. The fracturing channel opens, and fracturing fluid enters the formation through this channel to fracturing and modify that section. When multiple sections need to be treated, larger balls 22 are dropped sequentially, and the above operation is repeated, opening the sliding sleeves of each section step by step from bottom to top. After the sliding sleeve 3 is lowered into position, its lower damping claw 304 engages with the second damping claw groove 1801 of the lower connector 18, locking the sliding sleeve 3 in the open position to prevent displacement during subsequent retrieval operations.

[0048] During the ball seat retrieval stage, after all fracturing operations in all sections are completed, the retrieval anchor is lowered into the well using coiled tubing or drill pipe. When the retrieval anchor is lowered to the position of the sealing head 4, its pawl joint 20 engages with the left-hand sawtooth thread at the upper end of the sealing head 4, achieving a secure connection. Then, the retrieval string is lifted, and the second shear screw 10 is cut first. The sealing head 4 and the bridge body 9 move upward synchronously. The supporting effect of the lower outer circle of the sealing head 4 on the upper elastic claw plate 1501 of the elastic sleeve 15 is released. After losing the external support force, the elastic claw plate 1501 retracts inward, and its protrusion disengages from the first damping elastic claw groove 302 on the inner wall of the sliding sleeve 3. At this point, the entire inner ball seat unit is completely detached from the sliding sleeve 3. Continuing to lift the string will remove the inner ball seat unit from the well. Since the pawl joint 20 can continue to grip the sealing head 4 of the next stage sliding sleeve, the inner ball seat units of multiple stages of sliding sleeves can be retrieved in a single trip. After removal, the interior of the sliding sleeve is no longer limited by the inner diameter of the ball seat 21, achieving full bore and significantly expanding the production channel.

[0049] In the later control phase, after the inner ball seat unit is retrieved from the well, if it is necessary to seal or re-modify that section due to water production, low formation energy, or abnormal formation pressure, a dedicated closing or opening tool can be run into the well via coiled tubing. After the tool is lowered to the target sliding sleeve position, the centering block is positioned, and the locking block opens under hydraulic pressure and engages in the opening / closing tool slot 301 on the inner wall of the sliding sleeve 3. For sliding sleeves that need to be closed, the sliding sleeve 3 is pushed downwards to the closed position by lowering the tubing string, covering the fracturing through-hole 101; for sliding sleeves that need to be reopened, the sliding sleeve 3 is pulled upwards to the open position by raising the tubing string, exposing the fracturing through-hole 101. After the operation is completed, the flow rate is reduced to retract the locking block, and the tool can then disengage from the sliding sleeve 3 and be removed.

[0050] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this utility model is limited to these examples; within the framework of this utility model, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of this utility model as described above, which are not provided in the details for the sake of brevity. Any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A ball-launching fracturing sleeve capable of multi-stage series salvage and repeated opening and closing, characterized in that, include: The upper connector (1) and the lower connector (18) are fixedly connected to each other and form an outer shell, and the upper connector (1) and the lower connector (18) form cavities inside; A sliding sleeve (3) is slidably disposed in the cavity. The side wall of the upper connector (1) is provided with a fracturing through hole (101). The sliding sleeve (3) blocks the fracturing through hole (101) in the initial position. The inner ball seat unit, which is detachably disposed inside the sliding sleeve (3), includes a sealing head (4), a bridge body (9), an elastic sleeve (15), a connecting body (17), a ball seat (21), and a pawl joint (20) connected in series. The upper inner wall of the sealing head (4) is provided with a first left-hand sawtooth thread for docking with the anchor. The outer circle of the pawl joint (20) is provided with a second left-hand sawtooth thread that matches the first left-hand sawtooth thread on the inner wall of the next-level sliding sleeve sealing head (4) for realizing the series retrieval of multiple inner ball seat units. When encountering obstruction, it can be unscrewed by a right-handed tube column.

2. The ball-throwing fracturing sleeve capable of multi-stage series salvage and repeated switching as described in claim 1, characterized in that, The inner ball seat unit is detachably suspended inside the sliding sleeve (3) by the elastic sleeve (15); the upper end of the elastic sleeve (15) is circumferentially distributed with elastic claws (1501), and each elastic claw (1501) has an outwardly protruding boss at its upper end. The boss is initially engaged in the first damping elastic claw groove (302) provided on the inner wall of the sliding sleeve (3); the lower outer circle of the sealing head (4) opens the elastic claws (1501) in the initial state, so that the boss is engaged with the first damping elastic claw groove (302).

3. The ball-throwing fracturing sleeve capable of multi-stage series salvage and repeated switching as described in claim 2, characterized in that, The bridge body (9) and the elastic sleeve (15) are fixedly connected by a second shear screw (10); when the lifting is performed, the second shear screw (10) is cut off, the sealing head (4) moves upward relative to the elastic sleeve (15), the outer circle of the lower end of the sealing head (4) releases the spreading effect on the elastic claw (1501), the elastic claw (1501) retracts inward, the boss comes out of the first damping elastic claw groove (302), and the inner ball seat unit disengages from the sliding sleeve (3).

4. The ball-throwing fracturing sleeve capable of multi-stage series salvage and repeated switching as described in claim 3, characterized in that, The second left-hand sawtooth thread of the ratchet joint (20) has a sharp bevel angle and a small root angle, which is used to guide the ratchet joint (20) to smoothly enter the internal thread of the next sealing head (4) during normal lowering, and to ensure axial load stability after engagement.

5. The ball-throwing fracturing sleeve capable of multi-stage series salvage and repeated switching as described in claim 4, characterized in that, The circumference of the ratchet joint (20) is provided with an axially extending long groove, which divides the front end of the ratchet joint (20) into multiple circumferentially evenly distributed ratchet claw pieces. Each ratchet claw piece is provided with a groove to improve its radial elastic deformation capability.

6. The ball-throwing fracturing sleeve capable of multi-stage series salvage and repeated switching as described in claim 5, characterized in that, The lower end of the sliding sleeve (3) is cut with a long groove to form a circumferentially distributed damping claw (304); when the sliding sleeve (3) moves down to the open position after the ball is thrown and pressed, the damping claw (304) is engaged in the second damping claw groove (1801) provided on the inner wall of the lower connector (18) to prevent the sliding sleeve (3) from axial displacement when retrieving the inner ball seat unit.

7. The ball-throwing fracturing sleeve capable of multi-stage series salvage and repeated switching as described in claim 6, characterized in that, The sliding sleeve (3) is fixed inside the upper connector (1) by the first shear screw (7); when the ball (22) is placed on the ball seat (21), the first shear screw (7) is sheared by pressing the column to a predetermined pressure, and the sliding sleeve (3) slides down to expose the fracturing through hole (101).

8. The ball-throwing fracturing sleeve capable of multi-stage series salvage and repeated switching as described in claim 7, characterized in that, The inner wall of the sliding sleeve (3) is also provided with a switch tool slot (301), which is used to engage with the locking block of a special sliding sleeve opening or closing tool after the inner ball seat unit is retrieved from the well. The sliding sleeve (3) is moved axially by lifting or lowering the tubing string, so as to realize the re-opening or closing of the fracturing through hole (101).

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